Six brands of single-grip harvesters used in eastern Canada were studied working in softwood stands. Considerable variability in the length-measurement errors was observed. Much of the variability could be attributed to the operator, and specifically to the operator's ability to manage the measurement systems and use them correctly. Poorer results were observed where branchiness and stem defects were most pronounced. Under comparable, favorable conditions, all the heads in FERIC's study would be capable of producing logs for which 90% of the lengths would lie within a 10-cm range.